1-Wire diagrm with seperate Ground Rod

NEOHNEOH Solar Expert Posts: 74 ✭✭
I am helping a friend install a ground based Grid-Tie Solar Array. He called the Regional Electrical Inspector. The inspector stated that a DC Ground Rod must be installed at the location of the ground based Solar Array. Is the attached diagram the proper method for AC & DC Ground wires?

Attachment not found.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    Show the diagram to the Inspector and ask him if that's what he wants. His is the only opinion that matters because he's the one who stamps "approved" on the papers.

    That may sound like a cop-out, but there are a lot of differences of opinion about proper grounding even amongst those who know what they're doing (never mind bureaucrats).

    Were it me, I'd safety ground the PV frames/mounts at the array site and not connect it to the other ground (depending on the distance involved).
  • BB.BB. Super Moderators, Administrators Posts: 29,702 admin
    Re: 1-Wire diagrm with seperate Ground Rod

    Hmmm... I am not sure I would do it that way.

    Read the Inverter Manual closely about grounding. But, I would investigate connecting AC EGC to DC EGC at the GT inverter. And break path "C" and path "E".

    Next, review where the PV DC Disconnect (box #7) is located. If the Disconnect is on the Home, I would connect the metal case to safety ground "A" or "B" (just normal home wiring/grounding--nothing special).

    If the PV DC Disconnect is located near the array, I would connect its green wire ground to the New Ground Rod system. And the new ground Rod System should already be connected to the PV Array Mounting Structure as well as to the PV Metal Frames too.

    There should be no PV DC "-" (or "+" if positive ground) connection to earth/safety/metal in your wiring connections to ground except in the GT Inverter itself (should be pre-connected by factory through the NEC ground fault circuitry).

    You also have a "circuit" which appears to indicate an electrical connection(?). If so, then move the circle from "E"/PV Frame to New Ground Rod Ground cable and PV Frame (all framing and PV Frames should be same ground). Yes, you do have it connected at the "high side" of the array through "E"... And this is a "line drawing" and not a physical drawing--However, in the end, you want all lightning grounds to be short, heavy, rounded bends from their attach points back to the local ground rod. You don't want the PV Mount Ground to take a meandering path through the PV Frame grounds (even though, everything, presumable is metal to metal contact--the drawing sort of shows otherwise).

    What I do not like is bringing the Array Grounding back into the home and into the GT inverter (and PV Disconnect box if it is located on the side of the home). I do like the Underground ground-to-ground bond. That keeps both sets of ground at the same potential so that any fault currents have a solid connection back to the main/common well casing ground point.

    Basically, I would want all "grounds" to be local. If the "metal" is at/in/on the home, it should all be connected to the home ground. If the "metal" is at the array, it should all be connected to the array ground. And you already have a separate connection between home and array grounds (this is to trip fuses/breakers if there is an electrical fault--The rest of the grounding, in my humble opinion, is designed for lightning suppression which has different requirements/needs).

    Anyway, that is how I read your (very clear) diagram. Make sure you understand the pluses and minuses of the grounding and don't take one person's word.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    BB,
    Attached is diagram #1B.

    Some history ..
    The PV DC Disconnect must be mounted outside at the PV Array.
    The AC Disconnect must be located outside the home next to the AC NET Meter.
    The Inverter is mounted on a wall inside the home.
    The Inverter has it's own built-in AC/DC shutoff switch.
    The Inverter is located about half way between the AC Disconnect and the PV DC Disconnect.

    OK, we will disconnect the ground wire coming from the PV Array going into the Inverter.
    The PV DC Disconnect will have its own wire to the new DC Ground Rod.
    The 12 PV Panels will have a single continuous ground wire to the new Ground Rod.
    The PV Frame will have a single continuous ground wire to the new Ground Rod.
    All three above wires and Underground ground-to-ground bond are attached to the new DC Ground Rod.

    We will change the AC Ground to a single bare 6 AWG continuous wire, too.
    Start at the AC Panel through the AC Disconnect to both the Inverter's AC & DC Ground Terminals.

    Correct - NO external connection between PV Positive or PV Negative wire to GND.
    This is accomplished internally by the GFPD inside the Inverter - it is NEG ground.

    Better, in your opinion?

    Attachment not found.
  • BB.BB. Super Moderators, Administrators Posts: 29,702 admin
    Re: 1-Wire diagrm with seperate Ground Rod

    I am not a code guy--but it looks good for me.

    For cable "C"--you have a 6 awg wire documented--Does not connect any where (at least as I have suggested the connections). Could save money if the inspector will let you remove it from that run.

    For Cable "D", you will probably need to document the UL Style number for exterior / sun resistant cable. Something like "RHW-2/RHH (USE-2)". Also, will sections of "D" be in conduit?

    Also cables A thru C probably do not need 6 awg ground wire... 10 awg is probably "good enough" for code (use if it saves you some money).

    In our area, exposed "E" may need to be armored (copper wire in spiral steel flex).

    Probably about the extent of my knowledge of code... Please double check with somebody who knows your local code requirements better than I.

    If you are trenching, I would suggest laying a couple extra empty conduit or even 3-4" or larger black drain pipe. You can pull wiring/signal cable/water/etc. later if you need it without having to open another trench.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    i agree for you to talk it over with your inspector and if using an installer then talk to him first about it all. now i didn't go over this drawing or proposal from the beginning or for very long, but i believe the nec wants that ground wire to go back with the pv wires into the house or building where the ac inverter is at. doing this along with the underground ground wire to a ground rod as indicated could present some ground loops. i agree with how you are handling the ground, but code may not be on your side. inspectors may overturn the nec if they so choose to if they are knowledgeable enough to be convinced the nec goofed.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    Nice job on your diagrams! I notice that your inverter has: "DC GFPD (latching)".
    Would someone please explain to me what "latching" means in this context.
    thanks, vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    vtmaps,
    "Latching" means that if a Ground Fault is detected then the Inverter's AC Output will latch OFF. The Inverter will display a GND-FLT error code. The AC Output will stay off even after the Ground Fault condition is cleared (by the user or by itself). The Inverter must be manually shut-down and restarted after the Ground Fault is fixed to clear the GND-FLT error and to restart the AC output.

    This is similar to how a GFCI Outlet works. When a Ground Fault is detected the button pops out and it stays out - LATCHED OFF. The outlet will not restart until the user pushes the reset button which restarts AC output.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 1-Wire diagrm with seperate Ground Rod
    NEOH wrote: »
    "Latching" means that if a Ground Fault is detected then the Inverter's AC Output will latch OFF....
    Thanks for the explanation, It hadn't occurred to me that a GFPD could be nonlatching. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    Niel,

    " ... but i believe the nec wants that ground wire to go back with the pv wires into the house or building where the ac inverter is at ..."

    OK, We have modified the drawing, see #1C PDF attached. This time we have added a 6 awg bare Ground Wire from the Inverter DC EGC terminal directly to the DC Ground Rod outside. This is in direct conflict wth BB's suggestion. Therfore, we will fax PDF's 1A, 1B & 1C to the Electrical Bureau and ask which, if any, drawing they would approve regarding teh new DC Ground Rod. Their office is in another county not really local. Only conduit "c" is buried in the ground - from the house wall to below the DC Disconnect at the Solar Array. "e" is not a conduit, just quantity 4 of 6 awg bare wire attached to the DC Ground Rod.

    Attachment not found.

    BB,
    " ... For Cable "D", you will probably need to document the UL Style number ..."
    Cable "d" is not inside conduit it is "PV" type wire ...
    PV WIRE

    " ... Also cables A thru C probably do not need 6 awg ground wire ..."
    OK, we changed Ground Wires in conduit "a" and conduit "b" back to 10awg green in #1C PDF
    We thought a single 6 awg bare was capable of connecting all 3 points #1B PDF

    " ... For cable "C"--you have a 6 awg wire documented ..."
    Correct that was a typo in Wiring Scedule in #1B PDF - fixed.

    " ... In our area, exposed "E" may need to be armored (copper wire in spiral steel flex) ... "
    Since the Ground Based Frame was to be "enclosed", we thought exposed 6 awg bare to Ground Rod was OK.
    We will get advice from Bureau.
  • BB.BB. Super Moderators, Administrators Posts: 29,702 admin
    Re: 1-Wire diagrm with seperate Ground Rod

    It will be interesting to see what they say about the ground wire running from the array to the DC ground. I am not a fan of running separate grounds/remote array ground into the same box--but not the worst thing in the world ("C" ground wire will have to be insulated--will the inspector accept wrapping electrical tape on the bare copper pigtail as it enters the metal box(?)--in box "6"/inverter to prevent a ground loop in the metal box). Wonder what the AWG of this "ground fault sense" wire will be... Many inverters use a 1 amp fuse for ground fault detection--so a 6 awg wire is terrible overkill (and expense).

    Another issue--Cable "A" and "B" will probably have to have a white/neutral wire run with the 240 VAC line... The newer GT Inverter requirements need a white wire so that the inverter can monitor the LineA/LineB connections to ensure that the neutral to earth 120 VAC to neutral/ground does not go out of spec.). We had a new GT inverter (for awhile) that was retrofitted to our older installation--The "fix" there was to connect the white/neutral connection to the local green wire ground--Instead of pulling a new white wire. It is a bit silly to pull another 10 awg white wire that has only milliamps of current flow--but that is what the GT Inverter specifications plus building code rules usually require.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    BB,

    " ..."C" ground wire will have to be insulated ... "
    OK, we see that problem now.
    So, the Inverter's DC EGC wire can be changed to 10 awg insulated?
    And, the DC Disconnect's GND wire can be changed to 10 awg, too?
    We will add appropriate water tight connection upon exit for both from DC Disconnect #7, too.
    So, only the Frame and PV Array need to be BARE because of Multiple Grounding point connections.



    " ... Another issue--Cable "A" and "B" will probably have to have a white/neutral wire run with the 240 VAC line..."
    The AC Terminal Strip inside the Inverter only has ...
    [Line 1] [Line 2] [Ground]
    Where would we connect a WHITE neutral wire inside the Inverter?
    I am confused about that.
  • BB.BB. Super Moderators, Administrators Posts: 29,702 admin
    Re: 1-Wire diagrm with seperate Ground Rod
    NEOH wrote: »
    " ..."C" ground wire will have to be insulated ... "
    OK, we see that problem now.
    So, the Inverter's DC EGC wire can be changed to 10 awg insulated?
    "C" could be a 10 awg green wire. Connect it to the Ground Bus inside of the DC disconnect.

    6 AWG is only required for exposed/buried ground wires (large enough to survive physical damage). Although, in our area, "armored" 6 awg is required for exposed runs to the ground rod (as I understand).
    And, the DC Disconnect's GND wire can be changed to 10 awg, too?

    You may need 6 AWG if it is a direct run to the ground rod as you are not allowed to make splices in ground runs to to a ground rod--unless you use an approved method to connect the wires--like thermal welding (although 8 awg insulated may be OK--It has been 30 years since I looked at that section of code).
    So, only the Frame and PV Array need to be BARE because of Multiple Grounding point connections.

    Only because of the requirement of no splices in safety ground to ground rod. Does get a little crazy when trying to wire up multiple grounds to a solar array.

    I wonder, can you run a 6 awg wire from ground rod to first Ground Bond connection (in DC disconnect). Then run 10 AWG (even insulated green wire) from there to the array as needed (everything becomes a "branch" circuit--just like wiring up multiple motors/appliances. I have a feeling the AHJ will not buy that solution though.
    " ... Another issue--Cable "A" and "B" will probably have to have a white/neutral wire run with the 240 VAC line..."
    The AC Terminal Strip inside the Inverter only has ...
    [Line 1] [Line 2] [Ground]
    Where would we connect a WHITE neutral wire inside the Inverter?
    I am confused about that.

    Looking at page 14 of the manual (this PDF?), it appears they do their Line to "Neutral" measurements as Line to "green wire" ground. So, there would be no reason to pull an extra White/Neutral wire for this inverter.

    You might want to pull an extra white wire if/when the inverter is changed out years from now and they may need a white wire (although, on my system retrofit, they did just jumper the Neutral of the inverter to the green wire ground). Or, if the circuit is re-purposed to something else later (say hybrid inverter or generator transfer switch).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NEOHNEOH Solar Expert Posts: 74 ✭✭
    Re: 1-Wire diagrm with seperate Ground Rod

    Bill,

    From the PVP-3000 manual:
    ...
    The inverter/disconnect unit are connected by copper conductors and do not rely on conduit connections for bonding. All ground connections between the inverter cabinet and the disconnect cabinet are completed at the factory. During installation you will complete the ground connections by:

    * connecting the GEC from the PV System Array, and
    * connecting the EGC from the Main Utility Service Panel.
    ...

    The DC Ground connection is an "GEC" - Grounding Electrode Conductor.
    The AC Ground connection is an "EGC" - Equipment Ground Conductor.

    Do you agree with our conclusions given the above information ...
    The DC GEC Ground terminal is to be connected to the DC Ground Rod and must be an unbroken bare 6 awg wire.
    The AC EGC Ground terminal is to be connected to the ground bar in the Main AC panel and can be 10 awg insulated.

    What if we use a single continuous 6 AWG bare starting at the Inverter's DC GEC Terminal
    and then go though the Ground Terminal inside the DC Disconnect box
    and then end at the clamp on the new DC Ground Rod?

    Does this solve the issue you presented earlier regarding the bare 6 awg bare going through and touching the DC Disconnect box?

    Is there any issue with three different 6 awg bare wires ...
    Wire #1 = From the Inverter's GEC & DC Disconnect
    Wire #2 = From the 12 PV's
    Wire #3 = From the Frame
    all connected to the DC Ground Rod if each 6 awg bare wire has it's own clamp?

    Attached is the latest PDF #1E.
    note: The Inverter's "DC GEC" terminal was incorrectly labelled as "DC EGC" - fixed.

    Attachment not found.
  • BB.BB. Super Moderators, Administrators Posts: 29,702 admin
    Re: 1-Wire diagrm with seperate Ground Rod
    NEOH wrote: »
    From the PVP-3000 manual:
    ...
    The inverter/disconnect unit are connected by copper conductors and do not rely on conduit connections for bonding. All ground connections between the inverter cabinet and the disconnect cabinet are completed at the factory. During installation you will complete the ground connections by:

    * connecting the GEC from the PV System Array, and
    * connecting the EGC from the Main Utility Service Panel.
    ...

    The DC Ground connection is an "GEC" - Grounding Electrode Conductor.
    The AC Ground connection is an "EGC" - Equipment Ground Conductor.

    Do you agree with our conclusions given the above information ...
    The DC GEC Ground terminal is to be connected to the DC Ground Rod and must be an unbroken bare 6 awg wire.
    The AC EGC Ground terminal is to be connected to the ground bar in the Main AC panel and can be 10 awg insulated.

    I agree--that is what is intended by the MFG. And that would how UL/NRTL would have listed the equipment. To do different could make things "confusing" with the AHJ.
    What if we use a single continuous 6 AWG bare starting at the Inverter's DC GEC Terminal
    and then go though the Ground Terminal inside the DC Disconnect box
    and then end at the clamp on the new DC Ground Rod?
    I do not think you need to do that... Run 6 awg from the Array Ground Rod to the DC Disconnect Box Ground/Neutral Bus. Then run 10 awg (same rating wire as the PV +/-) from the DC Disconnect Ground Bus back to the Inverter's DC GEC.
    Does this solve the issue you presented earlier regarding the bare 6 awg bare going through and touching the DC Disconnect box?

    I believe that the DC GEC conductor still needs to be insulated when entering the Inverter Metal Box--You would not want the DC GEC (array ground) to short to the Inverter which (I presume) is mounted in/on your home. If there was a short between EGC and GEC--I don't think it will "break" anything. Instead you will run the risk of a "ground loop"... A ground path "through the box" sheet metal and through the 6 awg buried ground. Not recommended, but not the end of the world either.

    I believe the AC EGC is the "real" safety ground for the box (it is weird, both grounds are marked with the same symbol). I think the GEC is not a "real" ground but goes to the DC GFI detection fuse--and as such would not qualify as a "safety" ground bond. But, it is possible that both grounds are tied to the metal box too... I cannot tell from the documentation.

    Ah, from page 16 of the manual:
    Caution

    The DC/AC input and output circuits are isolated form the enclosure. The PV equipment ground conductor (EGC), where required by Sections 90-1, 90-2, and 690-43 of the National Electric Code (NEC), ANSI/NFPA 70, is the responsibility of the installer. Failure to properly install the ground conductor for the PV equipment can result in exposed metallic surfaces becoming energized to the full potential of the PV array.

    I guess the means that the EGC is "floating" in the Inverter enclosure.

    I don't like doing the connections this way as it could "bring" a lightning surge into the inverter/home. But the shorter path is still to the array ground rod...

    If you use the 10 AWG insulated wire for grounding the array (connecting at the DC Disconnect ground bus block)--it should not be a problem.
    Is there any issue with three different 6 awg bare wires ...
    Wire #1 = From the Inverter's GEC & DC Disconnect
    Wire #2 = From the 12 PV's
    Wire #3 = From the Frame
    all connected to the DC Ground Rod if each 6 awg bare wire has it's own clamp?

    I believe that is standard practice. Your AHJ will have final call.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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